The present invention relates to an apparatus for speed limitation of engines and/or for velocity limitation of engine-driven motor vehicles, having a controller that regulates the engine speed to an applied maximum permissible speed or regulates it to a speed that corresponds to an applied maximum permissible velocity.
In current production vehicles, speed limitation is accomplished by fuel blanking, i.e. if the predefined maximum permissible speed limit is exceeded, individual cylinders are shut down. The disadvantages of the this type of speed limitation system are that it is impossible to output a defined actual torque to external control units. Since combustion can no longer occur at the stoichiometric ratio when speed limitation has been instituted, emissions values deteriorate. In addition, the shutdown and initiation of injection occurring with such speed limitation systems cause severe torque surges, which result in a severe impairment of drivability.
German Patent No. 39 37 846 A1 describes an apparatus for speed limitation of engines having a controller for which, as a function of the difference between an actual speed value as controlled variable and a speed limit value, a torque setpoint (load torque) is defined as the manipulated variable. Also, German Patent No. 43 27 654 A1 and German Patent No. 44 34 022 A1, describe apparatuses for velocity limitation of engine-driven motor vehicles having a controller that correspondingly, as a function of the difference between an actual velocity value as controlled variable and a velocity limit value, defines a torque setpoint for the engine of the motor vehicle as the manipulated variable. These known apparatuses do achieve better drivability as compared to a cylinder shutdown system, but on the one hand disadvantages in terms of emissions values must be accepted, and on the other hand the resulting drivability has still not proven to be adequate.
An object of the present invention is to create an apparatus for speed limitation and/or velocity limitation that operates more smoothly and with better emissions values than conventional apparatuses, and can be utilized regardless of the type of engine used.
The present invention provides an apparatus for speed limitation of engines, having a controller (13) that, as a function of the difference (ndiff) between an actual speed value (nist) as controlled variable and a speed limit value or a speed limit function (nmaxeff), defines a torque setpoint (mvorg) for the engine as the manipulated variable. The controller (13) is equipped with means (10-12) for defining the torque setpoint (mvorg) as a function of the gradient (ngrad) of the controlled variable (nist). Means (11) for constituting a reduction torque (mred) as a function of the gradient (ngrad) of the controlled variable (nist) and of the actual torque value (mist) are provided. A subtraction stage (12), in order to constitute an anticipated torque (mvorh) from the difference between the reduction torque (mred) and the actual torque value (mist), is in working engagement with the controller (13) to define the torque setpoint (mvorg) as a function of the anticipated torque (mvorh).
The present invention also provides an apparatus for velocity limitation of engine-driven motor vehicles, having a controller (13) that, as a function of the difference between an actual velocity value as controlled variable and a velocity limit value or a velocity limit function, defines a torque setpoint (mvorg) for the engine of the motor vehicle as the manipulated variable. The controller (13) is equipped with means (10-12) for defining the torque setpoint (mvorg) for the engine of the motor vehicle as the manipulated variable. Means (11) for constituting a reduction torque (mred) as a function of the gradient (ngrad) of the controlled variable (nist) and of the actual torque value (mist) are provided. A subtraction stage (12), in order to constitute an anticipated torque (mvorh) from the difference between the reduction torque (mred) and the actual torque value (mist), is in working engagement with the controller (13) to define the torque setpoint (mvorg) as a function of the anticipated torque (mvorh).
With the torque-based speed limitation system and velocity limitation system according to the present invention, the controller is advantageously equipped with means for defining the torque setpoint as a function of the gradient of the controlled variable. In this context, means for constituting a reduction torque as a function of the gradient of the controlled variable and of the actual torque value, in particular by way of a characteristics diagram, are preferably also provided. A subtraction stage then serves to constitute an anticipated torque from the difference between the reduction torque and the acrual torque value. This is in working engagement with the controller in order to define the torque setpoint as a function of this anticipated torque. Influencing the torque setpoint by way of the gradient of the controlled variable, i.e. the actual torque value and/or actual velocity value, especially by way of the anticipated torque constituted according to the present invention, contributes substantially to the increase in drivability, and allows limitation to occur smoothly. The combustion processes occur at a stoichiometric ratio (lambda=1), so that good emissions values are maintained even while speed is being limited. Torque surges are prevented, which results in a considerable improvement in drivability for the driver of a motor vehicle.
Advantageously, a limit function stage is provided in order to constitute the speed limit function if the actual speed value exceeds a maximum continuous speed. This limit function stage preferably possesses a timing element for defining a maximum speed that exceeds the maximum continuous speed for a definable time period; a ramp generator is then provided in order to return the maximum speed to the maximum continuous speed after the definable time period. Allowing the maximum continuous speed to be exceeded briefly in this fashion also prevents torque surges, since it is thereby possible, by avoiding such torque surges, to return smoothly to the maximum continuous speed. This limit function stage thus prevents unpleasant surges even if the maximum continuous speed is exceeded as a result of a sharp rise in torque.
A subtraction stage is advantageously provided in order to constitute the difference between the speed limit function or the speed limit value and the actual speed value; this difference can then be conveyed to an input of the controller.
In order to avoid unnecessary control operations and to relieve stress on the controller, it is advantageous to provide a logic stage to constitute an anticipated value as a function of the gradient of the controlled variable and of the limit value or the limit function; a first comparison stage activates the controller if the controlled variable exceeds this anticipated variable and/or deactivates it if it falls below. This means that the greater the (positive) gradient of the speed or the velocity, the earlier the controller is activated. Because of this correlation with the gradient, the controller is optimally initiated or activated when such is necessary in order to prevent predefined limit values from being exceeded.
The logic stage can also, advantageously, have at least one second comparison stage that deactivates the controller if the controlled variable falls below a fixed value which is below the anticipated value. This ensures reliable shutdown of the controller if the difference between the controlled variable and the limit value has become sufficiently great.
A controller configured substantially as a PI controller is principally suitable for the speed limitation system or velocity limitation system. In this context, the torque setpoint constituted as the manipulated variable is provided in particular in order to intervene on devices for controlling the system regulating the delivery of air and/or fuel to the engine; acting on the air delivery system has proven to be particularly favorable. With an intervention of this kind, the combustion operations take place substantially at a stoichiometric ratio (lambda=1).
An exemplary embodiment of the present invention is depicted in the drawings and explained in more detail in the description below. In the drawings: